1. Field of the Invention
The invention relates to a support for a reflective target used in turbine casing bending measurements.
2. Brief Description of the Related Art
The assessment of clearance conditions in an operating turbine structure has proved difficult to achieve. Therefore WO 93/17296 provides apparatus which enables the clearance between seal fins on rotating blades and adjacent fixed structure, to be observed during rotation, and comprises refracting prisms on the fixed structure arranged so as to straddle sealing fin on the blades. The stage of blades on their associated disc are moved towards the fixed structure and light which is refracted through the prisms is attenuated by the fins. In one embodiment, the ratio of attenuated to unattenuated light intensity is utilized to generate electrical signals, which are then manipulated so as to indicate the magnitude of the clearance.
GB-A-1 080 726 discloses a method of testing the clearances between the tips of the blades of a bladed rotor and a casing within which the rotor is mounted, said method comprising directing light towards the region between the said tips and the casing in such a way that, as the rotor is rotated, at least part of the light periodically strikes the said tips so as to be affected by the radial positions of the latter, and employing the light which has been so affected to provide information concerning the sizes of the said clearances.
In DE-C1-196 01 225 a radial gap produced between the turbine housing and the turbine shaft or between the turbine housing and a turbine blade is monitored when a turbine is running. According to the invention, in order to ensure that the radial gap is measured constantly and accurately, a measuring reference point of non-oxidizing material is disposed on at least one turbine blade and/or on the surface of the turbine shaft in order to reflect light from a glass fibre probe which is guided through the turbine housing.
On the other hand other publications disclose different forms of the casing to avoid deformation. For example U.S. Pat. No. B1-6,336,789 discloses a casing for a steam or gas turbine comprises a shell and two flanges. The wall thickness of the shell is varied in an upper region facing away from the flange, in two central regions and in two lower regions facing the flanges, such that the upper region facing away from the flanges is reinforced in comparison with the lower regions facing the flanges. The lower regions facing the flanges are more flexible than the flanges which are attached by screws, and the partially reinforced central region and the reinforced upper region, and act as a joint to compensate for deformation, particularly in the radial direction. Consequently, the casing remains considerably more round in operation. The reduced radial clearance (achieved by reduced deformation) between the casing and the ends of the turbine blades leads to considerably increased efficiency during operation of the turbine
At the same time the surveillance can be done from the outside of the turbine casing. At this point the invention comes into action.